Articulated arms for supporting a load such as a lamp are well known, see U.S. Pat. Nos. 476,739 issued June 7, 1892, to Flaherty, 4,132,172 issued July 15, 1980, to Scattolin, 4,296,906, issued Oct. 27, 1981 to Matthijsse, 3,489,384 issued Jan. 13, 1970 to Perbal, 3,396,931, issued Aug. 3, 1968 to Eckstein, 3,391,890, issued July 9, 1968 to Perbal, 4,545,555, issued Oct. 8, 1985 to Koch.
Other such patents include Sapper, U.S. Pat. No. 3,790,773 issued Feb. 5, 1974, Eckstein, U.S. Pat. No. 3,396,931 issued Aug. 13, 1968, and Stryker U.S. Pat. No. 3,219,303 issued Nov. 23, 1965.
Jacobson U.S. Pat. No. 3,041,060, issued June 26, 1962, shows an articulated structure with a spring acting as equipoising means.
Jacobson U.S. Pat. No. 3,543,019, issued Nov. 24, 1970, teaches an articulated structure with "springs 15 and 16 mounted respectively on assemblies 4 and 5, to provide counterbalancing forces, so that the lamp will remain at rest in any selected position."
U.S. Pat. Nos. to Krogsrud, 4,160,536 issued July 10, 1979 and No. 4,080,530, issued Mar. 21, 1978, teach counterbalancing springs for articulated structures such as lamps and television sets.
U.S. Pat. No. 4,165,530 to Sowden teaches an articulated lamp structure with a spring 27. The entire structure is said to be balanced by resilient and frictional forces.
Two U.S. Pat. Nos. to Kirkeby, 3,239,184, issued Mar. 8, 1966 and 3,820,322 issued Oct. 18, 1966, provide structures including springs to counterbalance lamps.
The aforesaid patents make it clear that when an articulated arm supports a load, such as a lamp, the gravitational forces tending to destabilize the articulated arm are much greater when the load is at an extended lateral position, from the support for the articulated arm, than they are when the load is vertically above the support. Some of said prior art patents teach that a spring may be used to counterbalance those gravitational forces.